1. Field of the Invention
The disclosed invention relates to a method for measuring a minute current flowing through an electrical element, an inspection method of a semiconductor device employing the current measurement method, a semiconductor device employing the current measurement method, a semiconductor device employing the inspection method, a test element group (also referred to as a TEG), and the like. Here, a semiconductor device may be any device which works by utilizing semiconductor characteristics. For example, a semiconductor device widely includes the following elements: a semiconductor element (including a so-called power device) such as a transistor, a diode, and a thyristor, an integrated circuit such as an image sensor, a memory, and a converter, an integrated circuit including the above elements, and a display device and the like typified by a liquid crystal display device.
2. Description of the Related Art
In recent years, research on thin film transistors using In—Ga—Zn based metal oxide has been actively conducted (see Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2, for example). The research is proceeding with a view mainly to replacing silicon based thin film transistors used in display devices with thin film transistors using In—Ga—Zn based metal oxide.
By the way, in the case of manufacturing semiconductor devices that need charge retention, such as liquid crystal display devices, it is extremely important to know the characteristics of thin film transistors in an off state, e.g., the value of current flowing between a source and a drain of a transistor in an off state (hereinafter referred to as off-state current), and the like. This is because the parameters of a thin film transistor such as channel length and channel width are determined in accordance with the characteristics of the thin film transistor in an off state.
For now, it has been reported that the off-state current of a transistor using amorphous In—Ga—Zn based metal oxide is smaller than 1×10−14 A (see Non-Patent Document 3, for example).